Procedia Chemistry 4 ( 2012 ) 123 – 130

1876-6196 © 2012 Published by Elsevier Ltd. doi: 10.1016/j.proche.2012.06.018

Influence of Composite Electrolyte Membrane for Proton Exchange Membrane Fuel Cells

S. Handayania, , E.L. Dewib, J. Hardya, L. Christianib, Kurniawanb aDepartment of Chemical Engineering, Institute Technology of Indonesia, Jl. Raya Puspiptek Serpong, Tangerang, Indonesia

bAgency for the Assessment and Application of Technology, Center of Materials Technology, BPPT Gd. II, Lt. 22, Jl. M.H. Thamrin 8 Jakarta 10340, Indonesia

Abstract

The operation of proton exchange membrane fuel cell (PEMFC) under humidified condition using composite sulfonated polyether-ether ketones (sPEEK) membrane 1 is reported. Composite sPEEK membrane that were used in this report, have been produced and compared by additional of i.e. organic polymer (Acrylonitrile Butadiene Styrene) 2 and silica powder inorganic 3 to sPEEK polymer 1. Whereas, sPEEK 1, which is known as hydrocarbon polyelectrolyte membrane for PEMFC and direct methanol fuel cell (DMFC) to replace Nafion, has been the most used in both PEMFC and DMFC due to its good performance even though in low humidified condition it showed poor current density. Here we reported the effect of inorganic silica in hydrocarbon sPEEK membrane that contributes for a better water management system inside the cell, and showed 0.16 W/cm2 of power density which is 78% higher than that of non-silica modified. © 2012 Published by Elsevier Ltd. Keywords: Composite membrane; polyether-ether ketone; acrylonitrile butadiene styrene; silica, proton exchange membrane fuel cell.

1. Introduction

Proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cells (DMFC) using polymer electrolyte membranes are promising to be applied in portable device and transportation [1,2]. The most widely used class of membrane materials today for the PEMFC are of the perfluorinated sulfonic acid (PFSA) type, e.g., Nafion® (Dupont, USA), Flemion® (Asahi Glass, Japan), Aciplex® (Asahi Kasei, Japan), and derivatives thereof, such as the GORE-SELECT® membranes (W.L. Gore, USA). However, they have the disadvantage of being inherently expensive due to the complex fluorine chemistry involved

* Corresponding author. Tel.: +62-21-7561092 E-mail address: sri_handayani@iti.ac.id

Available online at www.sciencedirect.com

124 S. Handayani et al. / Procedia Chemistry 4 ( 2012 ) 123 – 130

in their fabrication and too expensive to extent their application [3,4]. Indeed, the Nafion based membrane shows complete domination in mechanical, physical and electrochemical properties. But there are some problems such as dehydration in high temperature and a high methanol permeability that caused the depolarization losses and energy conversion losses that could affecting the performance of fuel cells [5]. To solve this problem, many researches have been done developing alternative ways in finding more economical and efficient non-perfluorinated polymer proton exchange membranes. Many promising polymer are based on aromatic thermoplastic such as polysulfone, polyethersulfone, polybenzimidazole, polyether-imide, and polyether-ether ketone [6-10].

The polyether-ether ketone (PEEK) is an aromatic polymer in which 1,4-disubstituted phenyl groups are separated by ether (-O-) and carbonyl (-CO-) linkage. It was selected as polymer based membrane due to chemical resistance, good thermal stability, mechanical strength and adequate conductivity [10, 11]. In order to increase the hydrophilicity of polymer, polyether-ether ketone must be sulfonated using concentrated sulfuric acid to form sulfonated polyether-ether ketone (sPEEK). The process of sulfonation is being controlled by reaction time and temperature [10-14]. In the other hand, to increase proton conductivity properties of the membrane inorganic particles have been added into sPEEK 1. The hydrophilic inorganic materials were found to improve water uptake, which in turn leads to higher proton conductivity because water facilities proton conduction [8]. Some researchers conducted experiment by adding filler inorganic such as SiO2, Al2O3, ZrO in Nafion membrane to increase characteristic of electrolyte membrane like proton conductivity, mechanical strength and thermal stability and to decrease methanol permeability [15]. From this approach have been employed various filler to sPEEK i.e. tetraethoxy silane (SiO2), titanium oxide (TiO2), and zirconium oxide (ZrO2) [16].

The PEEK was selected as based polymer membrane due to good thermal stability and mechanical strength. PEEK is an aromatic, semicrystalline polymer which shows mild solubility in organic solvents due to its crystallinity. A. Carbone, et al. [17] showed the characteristics of sPEEK polymers are strongly influenced by the sulphonation degree. The sulfonation degree could controlled the PEEK properties while during crystalline is decrease then solubility would increase. sPEEK has been reported in the literature as a low cost alternate membrane for both PEMFC and DMFC applications [18,19].

Unfortunately, sPEEK with higher sulfonation degree and proton conductive also have higher water uptake and methanol permeability. There have been several attempts to overcome the excessive swelling while maintaining high proton conductivity, for example, by synthesizing sPEEK with various hydrophobic block: hydrophilic block ratios [20] and by blending the sPEEK polymer with non-conductive engineering thermoplastics (e.g., sPEEK+PEI, sPEEK+PES, sPEEK+PBI, sPEEK+ABS) [21-23] demonstrated blending sPEEK and ABS to reduce the methanol permeability in direct methanol fuel cell.

This paper was investigating proton conduction and water uptake properties of the blending sPEEK with various organic and inorganic filler to evaluate the potential for PEMFC and DMFC applications.

2. Experiment

2.1. Preparation of sPEEK 1

PEEK powder was dried in the oven at 60 °C for 3 h prior to sulfonation. An amount of 5 g of PEEK (Victrex, 450P) was dispersed in 100 mL of 95-97% sulphuric acid (pro analysis, Merck) maintaining under stirring for 3 h at 60 °C. After this reaction time the sulphonated polymers were precipitated in cold water, washed thoroughly to remove excess acid until the pH of the wash solution was ± 6 and completely dried.

125 S. Handayani et al. / Procedia Chemistry 4 ( 2012 ) 123 – 130

2.2. Preparation of composite membranes

For composite membrane 2 preparation, 3 g of sPEEK was dissolved in 24 mL N-methyl prylolidone (NMP) (pro analysis, Merck) and then added with 3 wt% of silica. Composite membrane 3 preparation was made by mixing 3 g of sPEEK and ABS mixture (from P.T. ARBE Styrindo & ABSii) with a ratio = 95:5 in 24 mL N-methyl prylolidone (NMP) for 24 h under stirring. The solution was then filtered and placed in ultrasonicator to remove air bubble that may still contained in the solution. After membrane casting, they were left to dry on a glass plate at 50 °C. The thickness of the membranes are approximately 70 - 90 m.

2.3. Characterization of membranes

XRD. The crystal structure of particles and membranes were investigated using X-ray diffractometer Shimadzu XD-610. SEM. The membrane morphology was investigated by field emission scanning electron microscopy in Philips XL-30 equipment. Samples were fractured in liquid nitrogen and sputtered with Au/Pd.

2.4. Proton conductivity

Ionic conductivity was measured using LCR (impedance capacitance resistance), impedance spectroscopy (HIOKI 3522-50 LCR HiTESTER) with various frequencies from 3 kHz to 1 MHz and 20 mV oscillating voltage. A conductivity cell was made up of two gold foils carrying the current and two gold wires sensing the potential drop, which was apart 1 cm. The fully hydrated sPEEK membrane with deionized water during 24 h was cut in 1 cm wide, 4 cm long prior to mounting on the cell. After mounting sample onto two gold foils on the lower compartment, upper compartment was covered, and then the upper and lower compartment were clamped as described by authors [24].

Fig. 1. Conductivity cell

The conductance of each membrane was measured at 25 C under fully hydrated condition. A conductivity cell was made up of two gold foils carrying the current and two gold wires sensing the potential drop, which was apart 1 cm as shown in Figure 1. The fully hydrated sPEEK membrane with deionized water during 24 h was cut in 1 cm wide, 4 cm long prior to mounting on the cell. After

Legend 1. Teflon cover 2. Thumbscrew 3. Teflon block 4. Open area to allow equilibration with environment 5. Membrane sample 6. Gold foil electrode 7. Gold wire

126 S. Handayani et al. / Procedia Chemistry 4 ( 2012 ) 123 – 130

mounting sample onto two gold foils on the lower compartment, upper compartment was covered, and then the upper and lower compartments were clamped as described by authors [18]. The proton conductivity ( ) of the membrane can be calculated using Eq. 1.

dwLG (1)

where G, L, w and d are conductance (S), the length between the electrode (cm), wide (cm) and thickness of the membrane samples (cm), respectively.

2.5. Membrane electrode assembly

Carbon supported platinum were prepared from commercial catalyst (ETEK Co.) 40 wt% Pt on optimized carbon (Pt/C). First, Pt/C was dispersed in Nafion solution followed by ultrasonic blending to achieve a uniform suspension. 2-Propanol-water (1:4) was added to a dilute catalyst ink were has obtained thus still in liquid phase. The catalyst ink obtained was coated on carbon paper as Gas Diffusion Layer (GDL) which supported by Micro Porous Layer (MPL) that were purchased from Gas Hub. Coating catalyst ink was done above a hot plate with temperature 60-80 C. Two carbon paper (supported MPL) which has coated with catalyst ink as GDL was pressed onto a treated composite membranes 2 and 3 like a sandwich to produce membrane electrode assembly (MEA). Hot pressing was done at temperature around 120 C and pressure 28 bar for 5 min.

2.6. Cell performance

Then each MEA were stacked into pairs of bipolar plate with parallel flow channel. Fuel cell test were carried out in a homemade 50 cm2 single cell with standard of Electrochem stack. The PEM fuel cell performance of the MEAs was tested by using in-house single fuel cell test set-up. Humidified hydrogen and oxygen gas were fed to the anode and cathode channel at 100 mL/min and 1 psi. The PEM fuel cell was operated at 50 ºC and connected to ProDigit 3310F DC Electronic Load. Schematics of experimental measurement are shown in Figure 2. The voltage (V), current (I), and power (P) were plotted as polarization curve.

Fig. 2. Schematics of system operation for measurement single cell PEM fuel cell [25]

127 S. Handayani et al. / Procedia Chemistry 4 ( 2012 ) 123 – 130

2.7. DMFC performance

All measurements were carried out by using two DMFC cells connected in series, which has 6.25 cm2 active area for each cell. Methanol 3% w/w is inserted into the DMFC system, waiting to be stable for about 30 min then the voltage and current value are measured. Methanol was used as fuel which is inserted directly into the fuel tank of DMFC kit. On the cathode, air is used as fuel (in this case oxygen) without using fan.

3. Results and Discussion

The nanostructure of membranes and its blends was investigated using X-ray diffraction scattering. The X-ray diffraction analysis sPEEK+Silika (sPEEK+Si) composite membranes 2 and also for sPEEK+ABS composite membranes 3 showed. All the blend and composite membranes show peaks at similar diffraction angles 2 as shown in Figure 4.

(a) (b)

Fig. 4. X-ray diffraction profile of (a) composite 2 sPEEK+Si and (b) composite 3 sPEEK+ABS

By looking at the results, the composite membrane 2 sPEEK+Si showed amorphous structure. ABS added in sPEEK make the membranes 3 have crystalline structure which decreases the water uptake. The basic homogeneous distribution of ABS within the sPEEK matrix can be observed from the SEM images of the sPEEK+ABS composite membranes 3 at magnification of up to 5000×, Figure 5 with the ABS content reaches 5%. Based on figure 5 it was found that both of sPEEK+ABS and sPEEK+Si are dense membrane but they have different morphology.

(a) (b)

Fig. 5. SEM cross-sectional images of composite membranes (a) sPEEK+Si (b) sPEEK +ABS

128 S. Handayani et al. / Procedia Chemistry 4 ( 2012 ) 123 – 130

Effect of membrane type on the proton conductivity can be seen in Table 1. The addition of hydrophilic particle could reach up the water uptake rather than additional of ABS. It is also indicates that silica particles is hygroscopic (easy absorb water). The increasing of water uptake of composite membrane sPEEK 2 that incorporating silica is followed by increasing of proton conductivity. The proton conductivity values of the composite membranes 3 sPEEK+ABS is given in Table 1, it is lower than proton conductivity of sPEEK+Si. This is due to the hidrophobicity polymer structure of ABS that slowing up the transport proton so it will decrease the proton conductivity as well.

Table 1. Thickness data, proton conductivity and water swelling of membranes

Membrane type Ionic conductivity (S/cm)

Water uptake (% w/w)

Methanol uptake (% w/w)

Membrane 1 sPEEK 0.018 15 24

Composite 2 sPEEK+Si 0.045 30 26

Composite 3 sPEEK+ABS 0.016 20 19

The observed fuel cell performances with composite membranes were compared and evaluated

by 5 cm2 PEM fuel cell and used H2/O2 at humidified conditions. As seen from Figure 6 that the value of I - V and I - P to sPEEK+Si membrane 2 is much larger than the membrane sPEEK+ABS 3. The highest power density for use sPEEK+Si composite membrane of 0.16 W/cm2 while for sPEEK+ABS 0.0034 W/cm2. This shows that the proton conductivity play an important role also in the PEMFC system.

Fig. 6. Polarization and power curves for the various MEA with different sPEEK+Si and sPEEK+ABS membranes in H2 /O2 at 50 C.

DMFC testing results of the two membranes can be seen in Figure 7. From these plots it can be observed that sPEEK+Si membrane achieved an output power value of 2.1 mW for 4.7 mA. However, the sPEEK+ABS membrane had even higher power than sPEEK+Si. This membrane achieved an output power value of 2.2 mW for 7 mA. It shows that the addition of ABS to sPEEK produce a better DMFC performance.

129 S. Handayani et al. / Procedia Chemistry 4 ( 2012 ) 123 – 130

4. Conclusion

Based on the results obtained for the PEMFC and DMFC tests, among the investigated systems reported here, the use of composite membranes either organic/inorganic or organic/organic can improve the performance of PEMFC and DMFC. For PEMFC, sPEEK supplemented with inorganic filler, in this study the inorganic filler is silica, was a good-quality composite electrolyte membrane. As for the DMFC, sPEEK + ABS polymer showed the best performance.

Fig. 7. Polarization and power curves for the various MEA with different sPEEK+Si and sPEEK+ABS membranes in of DMFC with 3% methanol fuel at the anode and air on the cathode

Acknowledgment

This work was conducted as a research from the National Strategic Grant 2011, No. 447/SP2H/PL/Dit.Litabmas/IV/2011, April 14, 2011. This program was funded by the Ministry of National Education of Indonesia.

References

[1] Kreuer K.D., J. Membr. Sci. 2001; 185: 29-39. [2] Savadogo O., J. Power Sources 2004; 127: 135-161. [3] Hoogers G., Fuel Cell Technology Handbook, CRC Press, USA, 2003. [4] Gubler L., Scherer G.G., Adv. Polym. Sci. 2008; 215: 1-14. [5] Fernandes A.C., Ticianelli E.A. J. Power Sources 2009; 193: 547-554. [6] Genova P., Domitrova B., Baradie D., Foscallo C., Poinsignon J.Y., Sanchez., J. Membr. Sci 2001; 185: 59-71. [7] Nolte R., Ledjeff K., Bauer M., Mulhaupt R., J. Membr. Sci. 1993; 83: 211-220. [8] Jones D.J., Roziere J., J. Membr. Sci. 2001; 185: 41-58. [9] Alberti G., Casciola M., Massinelli L., Bauer B., J. Membr. Sci. 2001; 185: 73-81. [10] Xing P., Robertson G.P., Guiver M.D., Mikhaelenko S.D., Wang K., Kaliaguine S., J. Membr. Sci. 2004; 229: 95-106. [11] Othman M.H.D., Ho S.L., Mustafa A., Ismail A.F., Organic/Inorganic Hybrid Membrane for Direct Methanol Fuel Cell

Aplication. The 3rd Regional Symposium on Membrane Technology for Industry and Enviromental Protection, ITB-Bandung, Indonesia, 2005.

[12] Mikhailenko S.D., Zaidi S.M.J., Kaliaguine S., Catal. Today 2001; 67: 225-236.

130 S. Handayani et al. / Procedia Chemistry 4 ( 2012 ) 123 – 130

[13] Li L., Zhang J., Wang Y., J. Membr. Sci. 2003; 226: 159-167. [14] Handayani S., Widodo W.P., Dewi E.L., Roekmijati W.S. Indonesian J. Mater. Sci. 2007; 8(2): 129-133. [15] Arico A.S., Baglio V., Di Blasi A., Creti P., Antonucci P.L, Solid State Ionics 2003; 161: 251-265. [16] Nunes S.P., Ruffmann B., Riwokowski E., Vetter S., Richau K., J. Membr. Sci. 2002; 203: 215-225. [17] Carbone A., Pedicini R., Portale G., Longo A., D’Ilario L.D., Passalacqua E., J. Power Source 2006; 163: 18-26. [18] Sambandam S., Ramani V., J. Power Sources 2007; 170: 259-267. [19] Handayani S., Dewi, E.L, Proton transport properties at high temperature of modified sulfonated polyether-ether ketone

membrane for direct methanol fuel cells application. Proceeding International Seminar on Chemistry 2008; OP028, 62: 152-156.

[20] Karthikeyan C.S., Nunes S.P., Prado L.A.S.A., Ponce M.L., Silva H., Ruffmann B., Schulte K., J. Membr. Sci. 2005; 254: 139-146.

[21] Manea C., Mulder M., J. Membr. Sci. 2002; 206: 443-453. [22] Zaidi S.M. J., Electrochim. Acta 2005; 50: 4771-4777. [23] Handayani S., Widodo W.P., Dewi E.L., Singgih H., Roekmijati W.S., Jurnal Teknologi 2007; 2: 85-164. [24] Sancho T., Soler J., Pina M.P., J. Power Sources, 2007; 169: 92-97. [25] Anis N., Wibowo W., Eniya L.D. Determination of Optimum Condition and Mass Transfer Hydrogen for single stack Proton

Exchange Membrane (PEM) Fuel Cell: Supported Pt/C as Electrocatalysis. International Conference on Fuel Cell and Hydrogen Technology 2009, October 28-29 Jakarta, Indonesia, 2009.